1. Type-safe Evolution of Spreadsheets
J´come Cunha
a Joost Visser Tiago Alves Jo˜o Saraiva
a
Universidade do Minho, Portugal, {jacome,jas}@di.uminho.pt
Software Improvement Group, The Netherlands, {j.visser,t.alves}@sig.eu
to be presented at FASE (ETAPS) 2011
17 – 21 January
J´come Cunha (UMinho-SIG)
a Type-safe Evolution of Spreadsheets 1 / 11

2. Motivation
Spreadsheets are notoriously error-prone;
Many errors are introduced when changing data;
But many others when changing the structure;
Models capturing the interdependencies between data can help
(inferable);
Co-evolution of models and instances.
J´come Cunha (UMinho-SIG)
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3. An Example
Budget for travel, hotel and local transportation expenses.
At the beginning of each year, it needs to be modified to
accommodate the next year;
Several steps are necessary:
add three new rows, labels, update formulas, etc.
Very prone to errors.
J´come Cunha (UMinho-SIG)
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4. An Example - Changing the Model
For expenses before and after tax, additional columns need to be
inserted in the block of each year.
The user needs to change all the year in the spreadsheet.
J´come Cunha (UMinho-SIG)
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5. ClassSheets: Specifying Spreadsheets
Erwig et al. have introduced ClassSheets to specify spreadsheets;
ClassSheets allow to express business object structures within a
spreadsheet using concepts from the OO paradigm;
J´come Cunha (UMinho-SIG)
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6. Modeling our Example
Class to represent a year;
Class to represent budget line;
Class to represent the relationship between them.
J´come Cunha (UMinho-SIG)
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7. Spreadsheet Models in Haskell
We have created a representation for spreadsheet models based on
ClassSheets;
Reused the 2LT framework: when specifying a model transformation,
we get for free functions to migrate data back and forward.
A, A data type and transformed data type
to
to witness function of type A → A
& (injective and entire relation)
Af A from witness function of type A → A
from (surjective, possibly partial)
from ◦ to = idA
We can compose refinements
J´come Cunha (UMinho-SIG)
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8. Spreadsheet Models in Haskell - References
References pose a particular challenge;
We implemented them as a pair of selection functions: one selects the
cell which is the reference and another select the referenced cell.
0sn
source source source Projection over type A
to identifying the reference
&+3 target Projection over type A
Af T A
identifying the referenced cell
from
source = source ◦ from
target .tp target
target = target ◦ from
J´come Cunha (UMinho-SIG)
a Type-safe Evolution of Spreadsheets 8 / 11

9. Evolution Rules
Combinators:
Pull up all the references: all references must be at the top level;
Apply after and friends: applies another rules after something;
Semantic:
Insert column: insert a new column;
Make it expandable: allows some part to be added more columns/rows;
Split: moves a column and substitutes it by references to the new
position;
Layout:
Change orientation: from vertical to horizontal and vice versa;
Normalize blocks: some results are not well formated;
Shift: shift vertically, horizontally, up or down.
J´come Cunha (UMinho-SIG)
a Type-safe Evolution of Spreadsheets 9 / 11

10. Make It Expandable
It is possible to make a block expandable:
id×head
-
(label : clas) (label : (clas)↓ )
l
id×tolist
Its implementation is as follows:
expandBlock :: String → Rule
expandBlock str (label : clas) | compLabel label str = do
let rep = Rep {to = id × tolist, from = id × head }
return (View rep (label : (clas)↓ ))
J´come Cunha (UMinho-SIG)
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11. Conclusions
We have created a safe representation of spreadsheet models (and
instances);
We shown rules for coupled evolution of models and instances;
We want to make this available for spreadsheet users;
We are working on an extension for OpenOffice;
J´come Cunha (UMinho-SIG)
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